Rechargeable energy storage system balancing

Abstract

A method and apparatus for electrical energy transfer between a pair of series connected batteries coupled between positive and negative DC rails of a power inverter operatively connected to a plurality of stator phase windings of a stator winding of a motor may include coupling a midpoint of the pair of series connected batteries to the stator winding of the motor, and controlling the power inverter to operate the power inverter and the stator winding as a switched-mode power converter to charge at least one of the stator phase windings from one of the pair of series connected batteries and to discharge the at least one of the stator phase windings to the other of the pair of series connected batteries.

What is claimed is: 
     
       1. A method for electrical energy transfer between a pair of series connected batteries coupled between positive and negative DC rails of a power inverter operatively connected to a plurality of stator phase windings of a stator winding of a motor, comprising:
 coupling a midpoint of the pair of series connected batteries to the stator winding of the motor; and 
 controlling the power inverter to operate the power inverter and the stator winding as a switched-mode power converter to charge at least one of the stator phase windings from one of the pair of series connected batteries and to discharge the at least one of the stator phase windings to the other of the pair of series connected batteries, 
 wherein coupling the midpoint of the pair of series connected batteries to the stator winding of the motor comprises closing a switch between the midpoint of the pair of series connected batteries and a respective phase terminal of one of the stator phase windings, and 
 wherein controlling the power inverter to operate the power inverter and the stator winding as a switched-mode power converter comprises interleaved pulse width modulation control of the power inverter. 
 
     
     
       2. The method of  claim 1  wherein the method is performed periodically during a DC fast charging cycle. 
     
     
       3. The method of  claim 1  wherein the method is performed upon completion of a DC fast charging cycle. 
     
     
       4. An apparatus for shuttling charge between a pair of batteries, comprising:
 the pair of batteries configured in series; 
 a motor including a stator winding having a plurality of stator phase windings commonly coupled at a neutral terminal and having respective phase terminals; 
 a power inverter having a plurality of phase legs coupled between positive and negative DC rails, the positive and negative DC rails coupled across the pair of batteries configured in series, and each phase leg including respective upper and lower solid-state switches with a respective phase pole therebetween coupled to a respective one of the stator phase windings at its corresponding phase terminal; 
 a switch between a midpoint node of the pair batteries configured in series and the stator winding, wherein the switch between the midpoint node of the pair of batteries configured in series and the stator winding comprises a switch between the midpoint node of the pair of batteries configured in series and the respective phase terminal of one of the stator phase windings; and 
 a controller: 
 operating the switch closed to couple the midpoint node of the pair of batteries configured in series to at least one phase winding of the plurality of stator phase windings; and 
 controlling conduction of the phase legs of the power inverter to operate the power inverter and the stator winding as a switched-mode power converter comprising at least one of the stator phase windings and one of the upper and lower solid-state switches of at least one of the phase legs, 
 wherein controlling conduction of the phase legs of the power inverter to operate the power inverter and the stator winding as a switched-mode power converter comprises interleaved pulse width modulation control of the power inverter. 
 
     
     
       5. The apparatus of  claim 4  wherein controlling conduction of the phase legs of the power inverter comprises controlling conduction of the respective upper solid-state switch of at least one phase leg to operate the power inverter and the stator winding as a switched-mode power converter wherein energy is transferred from the one of the pair of batteries between the midpoint node and the positive DC rail to the other one of the pair of batteries between the midpoint node and the negative DC rail. 
     
     
       6. The apparatus of  claim 4  wherein controlling conduction of the phase legs of the power inverter comprises controlling interleaved conduction of the respective upper solid-state switches of at least two phase legs to operate the power inverter and the stator winding as a switched-mode power converter wherein energy is transferred from the one of the pair of batteries between the midpoint node and the positive DC rail to the other one of the pair of batteries between the midpoint node and the negative DC rail. 
     
     
       7. The apparatus of  claim 4  wherein controlling conduction of the phase legs of the power inverter comprises controlling synchronous conduction of the respective upper solid-state switches of at least two phase legs to operate the power inverter and the stator winding as a switched-mode power converter wherein energy is transferred from the one of the pair of batteries between the midpoint node and the positive DC rail to the other one of the pair of batteries between the midpoint node and the negative DC rail. 
     
     
       8. The apparatus of  claim 4  wherein controlling conduction of the phase legs of the power inverter comprises controlling conduction of the respective lower solid-state switch of at least one phase leg to operate the power inverter and the stator winding as a switched-mode power converter wherein energy is transferred from the one of the pair of batteries between the midpoint node and the negative DC rail to the other one of the pair of batteries between the midpoint node and the positive DC rail. 
     
     
       9. The apparatus of  claim 4  wherein controlling conduction of the phase legs of the power inverter comprises controlling interleaved conduction of the respective lower solid-state switches of at least two phase legs to operate the power inverter and the stator winding as a switched-mode power converter wherein energy is transferred from the one of the pair of batteries between the midpoint node and the negative DC rail to the other one of the pair of batteries between the midpoint node and the positive DC rail. 
     
     
       10. The apparatus of  claim 4  wherein controlling conduction of the phase legs of the power inverter comprises controlling synchronous conduction of the respective lower solid-state switches of at least two phase legs to operate the power inverter and the stator winding as a switched-mode power converter wherein energy is transferred from the one of the pair of batteries between the midpoint node and the negative DC rail to the other one of the pair of batteries between the midpoint node and the positive DC rail. 
     
     
       11. An electrified vehicle, comprising:
 an electric propulsion system including a rechargeable energy storage system, a poly-phase electric motor having a stator winding having a plurality of stator phase windings, and a traction power inverter module including a motor controller and a power inverter; 
 the rechargeable energy storage system including a pair of batteries configured in series; 
 the power inverter having a plurality of phase legs coupled between positive and negative DC rails, the positive and negative DC rails coupled across the pair of batteries configured in series, and each phase leg including respective upper and lower solid-state switches with a respective phase pole therebetween coupled to a respective one of the stator phase windings at its corresponding phase terminal; 
 a switch between a midpoint node of the batteries configured in series and the stator winding, wherein the switch between the midpoint node of the pair of batteries configured in series and the stator winding comprises a switch between the midpoint node of the pair of batteries configured in series and the respective phase terminal of one of the stator phase windings; and 
 the motor controller: 
 operating the switch closed to couple the midpoint node of the pair of batteries configured in series to at least one of the stator phase windings; and 
 controlling conduction of the phase legs of the power inverter to operate the power inverter and the stator winding as a switched-mode power converter comprising at least one of the stator phase windings and one of the upper and lower solid-state switches of at least one of the phase legs, 
 wherein controlling conduction of the phase legs of the power inverter to operate the power inverter and the stator winding as a switched-mode power converter comprises interleaved pulse width modulation control of the power inverter.